1. Field of the Invention
The present invention relates generally to an active suspension control system for an automotive vehicle. More specifically, the invention relates to an improved working fluid circuit for an active suspension control system which is operable to provide control pressure effectively with reduced consumption of energy.
2. Description of the Background Art
Japanese Patent First Publication No. 62-295714 discloses an active suspension control system for an automotive vehicle. This system includes working cylinders each disposed between a vehicle body and a wheel, pressure control valves responsive to command signals to control working fluid pressure to be supplied to the working cylinders respectively, means for detecting or projecting a lateral acceleration acting on the vehicle body, and a controller responsive to a signal indicative of a lateral acceleration value to calculate command signals to the pressure control valves. The controller is operable to multiply the lateral acceleration value by control gains to provide the command signals which serve to suppress rolling motion of the vehicle.
In such a conventional system, working fluid at high pressure must be always supplied to a supply port of a pressure control valve such as an electromagnetic proportional pressure reducing valve for creating pressure in a working fluid cylinder against inertial force of rolling motion of a vehicle. Therefore, a great supply flow rate is necessary which is provided by a pressure source including a hydraulic pump and a reservoir tank for supplying high energy to the working fluid cylinders, resulting in great consumption energy. It will be noted that a vehicle incorporating a conventional active suspension control system consumes more fuel than a vehicle without an active suspension control system due to the additional energy consumed for anti-rolling motion control. Accordingly, an improved active suspension control system which conducts the same level of control as that of the conventional system, but with reduced energy consumption, has been sought.